This invention relates generally to a blood diluent and more particularly to a diluent that can be utilized in both automatic and semi-automatic systems for determining white blood cell populations, including two or more sub-populations of leukocytes.
Probably the most universally used medical diagnostic laboratory procedure is to analyze the blood of a patient for the purposes of determining the overall health of the patient as well as identifying specific intrusions into the body of an undesired nature. Two of the more important parameters studied in hematology analysis are red blood cell counts (erythrocytes) and white blood cell counts (leukocytes). The ability to differentiate sub-populations among the leukocyte group has become possible with recent advances in technology and is a particularly useful analytical tool.
Procedures for obtaining white blood cell counts vary from semi-automated procedures where preparatory steps are done manually prior to the actual counting done by single transducers, to completely automated procedures which employ sophisticated electronic circuitry capable of determining the form and size of a particular particle (i.e., cell) passing through a defined electrical field. U.S. Pat. No. 3,549,994 discloses an automated machine for hematology analysis and discusses the various factors to be considered in providing an automated system.
It has long been known that employing an aqueous solution of chemical salts will provide an electrolyte solution capable of conducting current to which a blood sample can be added for the purpose of diluting the erythrocytes and leukocytes as well as other blood components so as to enable the desired parameters to be observed, measured and counted. The general requirements for an effective diluent are: that it be capable of conducting an electric current; that it should stabilize the red blood cells enabling their volume to be unaltered and accurately measured; that it be nonreactive and have no adverse affect on white blood cells; and that it not interfere in any way with the conversion of hemoglobin to the cyanmethemoglobin form in which hemoglobin is best measured.
U.S. Pat. No. 3,962,125 discloses a multipurpose diluent for use in automated analytical equipment of the type broadly discussed above. The diluent disclosed in the reference patent includes inorganic salts, an organic chelating agent and a bacteriostat.
Another diluent of the prior art is disclosed in U.S. Pat. No. 4,346,018. The formulation set forth in this patent includes a mixture of organic salts, chelating agents, stabilizers and bacteriostats.
An improvement in lysing agents is the subject of U.S. Pat. No. 4,485,175. The system employed in this patent provides for a modified exposure of leukocytes which enables one to obtain a total of three populations, namely, lymphocytes, monocytes and granulocytes. According to the teachings of U.S. Pat. No. 4,485,175, it is necessary to employ a relatively expensive organic buffer in the diluent for use with the lysing agent disclosed in this patent in order to obtain the improved three leukocyte sub-populations.
The diluents of both the '018 and '175 patents discussed above require the use of cell stabilizers in order to maintain the integrity of the cells for a sufficient length of time to be counted and sized.
U.S. Pat. No. 4,213,876 sets forth a formulation for a novel diluent which utilizes a combination of inorganic salts sodium chloride, sodium dihydrogen phosphate and disodium phosphate, plus sodium sulfate anhydrous. The diluent set forth in this patent also includes, however, a combination of 8-hydroxyquinoline and procaine hydrochloride anhydrous which was found to be superior in terms of its stability and ability to suppress bubbles which have sometimes been a problem when bacteriostats are included in the formulation.